This invention relates to a slow release fertilizer containing oxamide and a process for the preparation of the same.
Oxamide [(CONH.sub.2).sub.2 ] is excellent as a component of slow release fertilizers owing to the low solubility thereof in water. To enhance the slow-releasing property of fertilizers, the fertilizers are generally preferred to be not powdered but granulated. To use the granular fertilizers, the fertilizers preferably have high hardness so as not to powder in the handling thereof. However, the oxamide is usually obtained in the form of a powder having a rigid surface, so that it is difficult to make the oxamide powder to adhere to each other to give a granular form. In the case that the oxamide is processed to form into spherical particles by industrially available granulating processes such as a rolling granulating process and a fluid granulating process, it is difficult to obtain a granular oxamide having a preferable hardness. The oxamide cannot be also granulated by a melt injection process, since the oxamide is decomposed under heating at a high temperature.
Japanese Patent Provisional Publication No. 59(1984)-169527 disclose a granular oxamide which comprises an oxamide powder bonded by polyvinyl alcohol in an amount of 0.2 to 10 wt. % of the oxamide powder, and a process for the preparation of the same which comprises granulating a mixture containing an oxamide powder and polyvinyl alcohol in an amount of 0.2 to 10 wt. % of the oxamide powder.
According to the process described in the above publication, there is obtained a granular oxamide having a shape of round bar at a length of 2 to 5 times as much as the particle diameter thereof (in an aspect ratio of 2 to 5). The granular oxamide has a particle diameter of 1.2 mm and a hardness of 0.6 to 1.9 kg. in the examples disclosed in the publication. The granular oxamide has such advantages that it has a hardness sufficient for handling, it is resistant to collapse in water and it hardly floats therein. Especially, the granular oxamide can be advantageously used as a component material of compound fertilizers.
However, the above-mentioned granular oxamide tends to have insufficient fluidity, because the shape thereof is a round bar, and in a certain case the insufficient fluidity thereof is unfavorable for mechanical fertilization. Further, the oxamide in such form is easily mineralized by action of soil microorganisms and hardly to give the slow release property, since the oxamide particle has a larger surface area per unit weight than that of a spherical particle due to its shape of round bar and is smaller in volume.